Every year Zuckerberg chooses a new goal. In 2011, for example, he vowed to only eat meat from animals he slaughtered himself. He's also tried to learn Mandarin and meet a new person every day.

Here's how he described his thank-you note resolution to Businessweek:

“It’s important for me, because I’m a really critical person. I always kind of see how I want things to be better, and I’m generally not happy with how things are, or the level of service that we’re providing for people, or the quality of the teams that we built. But if you look at this objectively, we’re doing so well on so many of these things. I think it’s important to have gratitude for that.”